1. Field of the Invention
The present invention relates to a radar sensor, more in detail to a receiving unit of radar equipment that radiates a transmission signal and receives a reflection signal from an object having reflected the transmission signal to thereby detect the presence and position of the object, and the moving speed of the object or the vehicle on which the radar is mounted, and so forth, specifically to a radar sensor that uses a millimeter wave or sub-millimeter wave signal more than 20 Ghz to the transmission signal.
2. Description of the Related Art
Radar equipment has been widely used which radiates an electromagnetic wave and receives a reflection wave from an object that has reflected the electromagnetic wave to thereby detect the object, (hereunder, radar equipment is simply called radar). In recent years, a super high frequency signal such as a millimeter wave or a sub-millimeter wave is applied to this electromagnetic wave. As a typical example of the radar using this kind of millimeter wave, there is the on-vehicle radar applied to a warning system for a distance between vehicles.
In most of millimeter wave modules used to these systems, an active circuit including an oscillator and a mixer and so forth is mounted on a base plate, which is hermetically sealed into a conductive package in order to shield external noises. Discrete components such as diodes are used as the elements of the active circuit, however in recent years an MMIC (Monolithic Microwave Integrated Circuit) is utilized in order for miniaturization and lighter weight and so forth.
However, hermetically sealing by the conductive package requires placing the antenna outside the conductive package, which leads to a problem of expanding the size of the module. Further, the active circuit inside the conductive package must be connected to the external antenna, which also gives a problem of being not suitable for cost reduction of the module. A technique to solve these problems is disclosed in Japanese Patent Laid-open No. H11-4118, for example. According to the technique as shown in FIG. 5, the active circuit 25 and the antenna 24 are mounted on one plane of the base plate 26, which is mounted on one metal base plate 21. In case of FIG. 5, the antenna 24 is formed on the base plate 26. And, a radiation window 22 from which the antenna 24 radiates electromagnetic waves is provided over the antenna 24. The radiation window 22 is formed with a nonconductive material, and is welded to the conductive package 23 for hermetical sealing. The radiation window 22 also functions as a dielectric lens that condenses the electromagnetic waves into a desired beamwidth.
In the on-vehicle radar and so forth, reduction of the production cost as well as miniaturization of the unit becomes extremely important. The foregoing conventional technique is suitable for miniaturization, but the radiation window has to be provided to the conductive package, and the radiation window and the conductive package have to be welded for sealing hermetically; thus it has a still more complicated packaging structure and more manufacturing processes. Accordingly, the conventional technique involves difficulty in achieving a millimeter wave radar sensor at a low production cost.
An object of the invention is to achieve a radar sensor that operates in the millimeter wave ranges at a low cost in a small size.
In order to accomplish the foregoing object, in the radar sensor of the invention, an antenna and an active circuit including an oscillator coupled to the antenna and a mixer, etc., are made up into an MMIC (Monolithic Microwave Integrated Circuit), and the MMIC and the antenna are sealed with a resin package.
One preferred embodiment of the invention has a lens formed on a part of the resin package near the antenna. The lens may be formed integrally with the resin package by using the same material as that of the resin package, or it may be formed to be replaceable.
The active circuit and the antenna can be made up with plural MMIC chips and the antenna, but a necessary active circuit may be formed into one chip MMIC.
Further, the antenna may be formed on one semiconductor substrate together with the active circuit, and the antenna and the active circuit may be formed into one chip.
According to the invention, generally the resin package can be formed by a metal mold, which remarkably reduces the manufacturing cost; and being non-conductive, the resin package does not need to provide a special structure such as a radiation window over the antenna. From this point, it is suitable for reduction in costs.
Especially, in case of achieving a radar sensor that radiates a high frequency signal more than 20 GHz and receives a reflected signal from an object that reflected the high frequency signal, providing the resin package with a dielectric lens will decrease the area for a planar antenna as a microstrip patch antenna to make the radar sensor small accordingly, and also facilitate the setting of beamwidth of the radio wave from the antenna. In case of the planer antenna as a microstrip patch antenna, generally plural antenna elements synthesize powers to attain a desired beamwidth. Since the area of IC is proportional to the cost, the number of antenna elements should be small. Therefore, the radar sensor of the invention takes on a construction that attains a desired beamwidth by providing a few antenna elements (extremely, one element) and mounting a dielectric lens over the antenna.
In case of making a dielectric lens and a resin package separately and making a radar sensor by adhering these, producing the dielectric lens in plural shapes, selecting the most suitable one according to the application used, and adhering the selected one to the resin package will attain a radar sensor suitable for each application.
The relative permittivity of a material for the dielectric lens and the resin package should be about 3 to 6, from the viewpoint of lens size.